1. Field of the Invention
The present invention relates to a method of restarting sequentially controlled equipment installed in a production line when the equipment is out of order. The equipment is restored to the normal condition after the cause of a failure is removed. The present invention also relates to a system for effecting such a method.
2. Description of the Related Art
According to a known sequential program control, each step of the control is sequentially executed according to the program which specifies the order for operating each output element, for example an actuator, constituting the operation system of equipment. An apparatus for monitoring whether or not the sequential program control is in order is proposed in, for example, Japanese Laid-Open Patent Publication No. 60-238906. According to this disclosure, operation patterns of elements constituting a sequential control circuit which can appropriately operate the equipment are initially stored in a memory. It is sequentially checked whether or not the operation patterns of the elements in operation coincide with those stored in the memory. If both of them do not coincide with each other, it is judged that the operation system has caused a failure.
In the event of a failure of the operation system of the sequentially controlled equipment, the operation of the equipment is suspended. In order to automatically restart the equipment after a defective portion is restored to the normal condition, it is necessary to manually return all output elements constituting the operation system to respective restorable operation steps, i.e., the so-called home positions, at which the output elements are capable of restarting without interfering with one another.
However, the home positions of all the output elements are generally set only to respective operation steps corresponding to the initial condition of the equipment. Therefore, when the failure occurs in the equipment at a certain later operation step in sequential operation steps, it takes a long time to return each output element to the home position (initial condition) thereof. Thus, much time is wasted before the equipment restarts operation.